Throughout this application, various publications are referenced by author and date. Full citations for these publications may be found listed alphabetically at the end of the specification immediately preceding the Sequence Listing. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art as known to those skilled therein as of the date of the invention described and claimed herein.
Members of the family of cysteine proteases related to the interleukin 1β converting enzyme (ICE) have been shown to be necessary for programmed cell death in a number of biological systems (Yuan et al., 1993). For example, mutations of the ICE homologue, ced3, inhibit cell death which normally occurs during development in C. elegans (Hengartner et al., 1992) and overexpression of ICE or the ICE-like proteases NEDD-2/ICH-1 and Yama/apopain/CPP32 induces apoptosis in primary neurons, rat fibroblasts and insect cells (Gagliardini et al., 1994; Miura et al., 1994; Wang et al., 1994; Kumar et al., 1994; and Fernandes-Alnemri et al., 1994). Mice lacking ICE are resistant to apoptosis induced by Fas antibody. In the mammary gland, ICE mRNA is expressed during involution, when apoptosis occurs in this tissue. The pox virus product crmA, a serpin-like pseudosubstrate for ICE, protects sensory neurons and fibroblasts from trophic factor withdrawal-induced death (Gagliardini et al., 1994 and Miura et al., 1994), while Fas/APO-1 mediated apoptosis is blocked by the inhibitory peptide YVAD (Seq. I.D. No. 7), as well as crmA (Tewari and Dixit, 1995; Enari et al., 1995; Los et al., 1995; and Tewari et al., 1995). Normal motor neuron loss in development is also blocked by YVAD (Seq. I.D. No. 7), a pseudosubstrate which mimics the pro-IL-1β cleavage site and thus inhibitis ICE-like proteases (Milligan et al., 1995). While ICE cleaves pro-IL-1β to produce IL-1β, the role of IL-1β itself in apoptosis is unresolved and it has been suggested that other substrates may be critical in cell death (Lazebnik et al., 1994; Tewari et al., 1995; and Nicholson et al., 1995).
Although many researchers have focused their efforts on the identification and isolation of an inhibitor of the family of cysteine proteases related to the ICE enzyme, there has been little success in this area. Many of these research strategies involve searching through a multitude of compounds and agents which are extrinsic to the ICE protein normally. However, the present invention deviates from the established search strategies and provides for the surprising discovery that use of a piece of the ICE enzyme itself successfully inhibits ICE and thus prevents neuronal cell death.